Apparatus and method for continuous drying



arch 28, 1967 E. L. FRITZBERG 3,310,881

APPARATUS AND METHOD FOR CONTINUOUS DRYING Original Filed Jan. 14. 1965 I N VEN TOR. EDWAROLFRITZBEKG yawmw ATTORNEY United States Patent 3,310,881 APPARATUS AND METHOD FOR CGNTINUOUS DRYING Edward L. Fritzherg, Minneapolis, Minn, assignor to The Pillsbury Company, Minneapolis, Minn, a corporation of Delaware Continuation of application Ser. No. 425,533, Jan. 14, 1965. This application Mar. 14, 1966, Ser. No. 534,247 14 Claims. (Cl. 348) This application is a continuation of my prior application Ser. No. 425,533, filed Jan. 14, 1965, and now abandoned.

This invention relates generally to apparatus for methods for the continuous drying of various moist particulate or granular material by so-called quench drying. More particularly, the invention relates to apparatus and methods for continuous drying of moist food or similar organic materials in hot oil under partial vacuum.

According to known quench drying processes as for example in Patent Numbers 3,261,694 and 3,239,946 and patent application, Ser. No. 157,478, a large number of moist food products and similar materials have been dried to as low as from about /2 percent to 5 percent moisture by introducing the material into a bath of hot oil having an initial temperature within the range of about 240 F. to 600 F. under a partial vacuum of the order of about 22 to 29 inches of mercury. Initial rapid heat transfer from the hot oil to the moist material causes an evolution of moisture from the material to be dried and rapidly drops the temperature of the oil. Dehydration is then usually continued to completion under somewhat lower temperature conditions. After the drying is completed at the lower temperature level, the excess oil is separated from the dehydrated product. This method produces high grade dehydrated products which do not collapse, but tend to retain their original size and shape and are generally superior in flavor, texture, etc., to products dehydrated by vacuum evaportaion or other conventional methods.

Because of the sudden expansion of the materials due to the rapid evolution of vapors when the moist material comes into contact with the hot oil, the volume of the quench drying chamber must be at least three times the total volume of the solid and liquid components. In the past quench drying has been carried out in batches. The three-fold or more increase in volume of the materials requires the use of a large batch drying chamber in order to obtain commercially feasible production yields. As the size of the batch is increased, not only the size of the drying chambers, but pumps, heat exchangers and the like increase correspondingly. This not only places a practical limit on the size of batch which can be handled, but tends to increase the required capital investment to uneconomic levels.

The principal object of the present invention is to avoid the disadvantageous alternatives of the batch process, of small production yields or large capital investment, by providing an apparatus and method for continuous drying of moist material in hot oil under partial vacuum.

It is a further object of the present invention to provide an apparatus and method by which hot oil and moist feed material are continuously blended in the desired proportions in an entrance to an expansion chamber, fashioned in the general configuration of a cyclone separator, where the mixture expands rapidly and flows With great velocity into the expansion chamber Where the vapors are separated from the liquid and solid components.

It is a further object of the invention to provide an apparatus and method in which additional drying of the feed material may take place in the bottom of the ex- Patented Mar. 28, 1967 pansion chamber before the liquid and solid components are removed continuously through a vacuum-tight seal for separation of the excess oil from the solids by centrifugal force.

It is a still further object of the present invention to provide a method and apparatus for quench drying in which the moist material and hot oil are blended in the entrance to an expansion chamber, and the thusly initially dried material is subjected to a secondary drying stage in which it is further contacted with hot oil.

Other objects of the invention will become apparent as the description proceeds.

To the accomplishment of the foregoing and related ends, this invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the invention may be employed.

The invention is illustrated by the acompanying drawings in which the same numerals refer to corresponding parts and in which:

FIGURE 1 is a schematic representation of a quench drying system utilizing a cyclone separator as an expansion chamber;

FIGURE 2 is a fragmentary horizontal section on the line 22 of FIGURE 1 and in the direction of the arrows; and

FIGURE 3 is a further schematic representation of a quench drying system utilizing a cyclone expansion chamber and including a secondary drying stage.

Referring now to FIGURE 1, there is shown a hopper 10 which serves as a feed inlet for the material to be dried. Hopper 10 communicates through a vacuum-tight feed mechanism, such as a star valve or screw conveyor, with a mixing chamber 12. The mixing chamber 12 is in the form of a conduit or pipe communicating with the entrance port 14 (preferably tangential) to the upper portion of a cyclone separator 15 of conventional configuration. Hot oil is introduced into the mixing chamber 12 from an inlet 16 through which the oil is pumped from a heat exchanger 17 or other heating means for the oil. The hot oil is desirably sprayed under pressure or atomized into the mixing chamber.

The feed material is entrained in a high velocity stream of oil. Upon contact of the oil and material to be dried there is a rapid expansion and flow of the entrained material at high velocity through the mixing chamber through port 14- into cyclone 15. A stack 18 extends through the top of the cyclone 15 to connect the cyclone with a vacuum system and condenser in the conventional manner for the maintenance of partial vacuum within the maxing chamber 12 and cyclone 15 and for withdrawing the vapors evolved. The stack 18 desirably extends into the cyclone below the level of port 14 to function as a battle and prevent the withdrawal of solid product along with the evolved vapors.

The major expansion of material occurs within the upper portion of the cyclone 15. The evolved vapor is withdrawn and the partially dehydrated material and oil descends by gravity to the bottom end of the cyclone cone where it collects in a mixed oil-solid bath 19. The bottom portion of the cyclone cone is desirably encased in a jacket 29 through which hot oil, steam or other heat transfer medium may be circulated to control the term perature of the bath 19. For example, hot oil from the heat exchanger 17 may be circulated through a line 21 to the jacket and then recycled through a line 22 to pump 23 and back to the heat exchanger 17.

Additional drying of the moist material may take place in the bottom of the cyclone cone in bath 19 because of the heat supplied through the temperature control jacket and the regulated holding time. The holding time is controlled by means of the discharge rate of the materials. The liquid and solid components are removed continuously from the bottom of the cycline through a vacuumtight seal 24, such as a star valve or rotary discharge means, and through any suitable conduit, indicated schematically at 25, to a conventional vacuum-tight continuous centrifuge indicated at 26. The excess oil is thrown off and collected and returned through line 27 to pump 23 for recycling through the system. This oil being cooler may be passed through line 2% for blending with hot oil in line 2 1 for regulating the temperature in jacket 29, or may be returned through heat exchanger l7 through line 16 and returned to dryer. The drives of the feed mechanism 11 and outlet mechanisms 24 and 43 may be interlocked to assure a continuous constant how of material through the system. The dry product is dis charged at 2.3 through a vacuum-tight sealing means 43.

Where necessary because of the buoyancy of the partially dehydrated solids, the material may be urged to the bottom of the cyclone by means of a slowly rotating lightweight and preferably foraminous screw feeder h whose shaft 51 is supported at one end in a spider 52 and which extends through stack 18 through an appropriate seal and is driven by drive means 53. The drive means preferably is an electric motor and reducing gear box to cause the screw feeder to be rotated relatively slowly so as to permit retention of the material sulficiently long for complete dehydration. The screw feeder need extend only part of the way toward the bottom of the cyclone leaving ample room for free collection of the oil and solids in bath 19.

Referring now to FIGURE 3, there is shown in schematic form a related continuous vacuum drying system incorporating a cyclone expansion chamber as already described, along with a secondary vacuum drying stage. As already described, the material to be dried is fed through hopper 1d and vacuum-tight seal 11 into a mixing chamber 12 where it is entrained in and contacted by hot oil from inlet pipe d6 for expulsion through port 14 into a cyclone chamber 15 maintained under partial vacuum. Here the moisture evolved during the rapid expansion of the materials is drawn off through stack 18, which in turn is connected with a conventional vacuum system and condenser. The partially dried solid material and oil accumulates in a bath 19 at the bottom of the cyclone chamber and is discharged continuously through a vacuum-tight seal and feeder 24- into a secondary drying chamber 33.

Secondary drying chamber as illustrated schematically is an elongated horizontal axis chamber having a horizontal shaft 31 extending therethrough and carrying a helical screw product propelling means 32 for moving the solid material through the chamber. It is fitted with a perforated false bottom 33 which supports the solid material while permitting a large part of the oil to drain through for collection in a sump and recycling through a line 35 through pump 23 to heat exchanger 17. The secondary vacuum drying chamber is also provided with a stack 36 for connection to a vacuum system and condenser for maintenance of partial vacuum within the chamber and for withdrawal of the further evolved vapors.

A further hot oil supply line 37 supplies hot oil from heat exchanger 17 to a plurality of spray head or atomizers 38 disposed alongthe length of chamber 30. Thus, the partially dried material from cyclone chamber 15 is fed continuously into chamber 30 where it is subjected to continued partial vacuum and contacted with hot oil for further evolution of vapor and expansion.

The material is advanced through chamber 30 by means of the screw conveyor 32 to a discharge duct 39 opposite from the entrance to chamber 30. The dried material is largely drained of oil in the course of its passage through chamber 30. It is discharged through a vacuum-tight sealing means 40 and thence through a conduit, indicated schematically at 41, to a vacuum-tight continuous centrifuge 26 where the remaining oil is separated and discharged through line 27 for recycling while the dried product is discharged through vacuum-tight sealing means 43 at 28 for further processing, or storage, or packaging. Temperature of the hot oil introduced into the secondary drying chamber 36 may be controlled by introducing cooler oil from discharge line 35 and pump 23 through line 42 into inlet line 37. The drives of scaled feeder 11 and discharge means 24, 40 and 43 may be interlocked to insure uniform continuous flow of material through the system.

The drying processes of the present invention are adapted to the dehydration of a large number of products, among which may he mentioned fruits, berries, vegetables, nuts, cereals, meats, poultry, fish, other sea food, bakery products, condiments and the like. These materials may be preliminarily prepared by washing, peeling, pitting, cutting to size, etc., as appropriate. In some instances they may be preliminarily dried, as in hot air, or precooked, candied, glazed or pickled, or the like. They may be frozen, or unfrozen at temperatures up to room temperature. When frozen, they may be introduced to the drying system typically at a temperature anywhere from about 40 F. to +20 F.

The material is introduced in particulate form. It may be in the form of granules, or chunks, or flakes, or the like whose average dimensions range between about .4 inch and 1 inch. The moist material is generally dried to from about /2 percent to 5 percent remaining moisture. The initial moist material is generally admixed with hot oil in the ratio of from about 4 to 40 parts by Weight of moist solid material to each parts by weight of hot oil.

A large number of animal and vegetable oils, and mixtures thereof, may be used. These include, for example, fish oil, lard, butter oil, corn oil, cottonseed oil, olive oil, peanut oil, coconut oil, chicken fat, hydrogenated oils, ethyl esters of fatty acids, and the like. Desirably oils having melting points between about 100 F. and F. are used. The drying system is operated under an applied partial vacuum within the range of about 22 to 29 inches of mercury.

The material to be dried is introduced into the mixing chamber at its normal temperature, be it frozen or unfrozen. The oil is introduced to the mixing chamber at an elevated temperature between about 240 F. and 600 F. and preferably between about 325 F and 440 F. The initial heat exchange and evolution of vapor occurs rapidly within about /2 and 4 minutes. The total residence time of the solid material to completion of dehydration will typically range from about 10 to 40 minutes.

After the initial high temperature evolution of moisture, the dehydration may be carried to completion at a lower temperature in the range between about 180 F. and 230 F. In the system illustrated schematically in FIGURE 1. dehydration is completed by prolonging the residence time in the bottom of the cyclone flash chamber in which the temperature is regulated by means of the jacket surrounding the bottom of the cyclone cone. In the embodiment of FIGURE 3, the residence time in the cyclone flash chamber is shorted and dehydration is completed in the secondary drying chamber.

The operation of the system shown in FIGURE 1 is illustrated by the following typical example. Chicken meat cut into approximately A inch chunks and frozen is introduced into the feed hopper at approximately 0 F. The cyclone chamber is evacuated to about 28 inches of mercury. The frozen chicken meat is entrained in a stream of hot chicken fat at a temperature of about 375 F. The meat and oil are fed continuously in the pro portion of about 30 parts by weight of meat to each 100 parts of'oil. An immediate expansion and evolution of "moisture occurs forcing the mixture at high velocity out about 225 F. by heated oil circulating through the cyclone jackets. The liquid-solid mixture is continuously withdrawn from the bottom of the cyclone at a rate equal to the feed. rate after an average residence time within the cyclone of about minutes. This material is then centrifuged to subject the material to between 100 and 600 Gs, and preferably between 150 and 250 Gs, to remove the excess oil. The resulting product has a moisture content of the order of about 3 percent. It has maintained substantially the size, shape and overall appearance of the feed material with relatively little damage and has a dry appearance with an almost imperceptible oily feel. The product is useful, for example, for incorporation into soup mixes and the like.

The operation of the system of FIGURE 3 may be illustrated as follows. Fresh diced potatoes at room temperature are introduced into the feed hopper and entrained in corn oil at a temperature of about 350 F. in the proportion of 1 part by weight of potatoes to 5 parts of oil and introduced into the cyclone maintained at about 27 inches of mercury partial vacuum. Spontaneous expansion and evolution of moisture occurs in the mixing chamber, ejecting the mixture at high velocity into the cyclone chamber, where further expansion and evolution of moisture and cooling of the mixture occurs. As the potato particles absorb oil and become less buoyant they sink to the bottom of the cyclone along with excess oil and the mixture is continuously withdrawn to the secondary drying chamber. The total residence time in the cyclone is of the order of about 5 minutes. This mixture of cooled oil and partially dehydrated potatoes is then subjected to the partial vacuum of the secondary drying chamberp Oil maintained at a lower temperature of about 200 F. by blending with cooler oil from the secondary drying chamber is introduced through the spaced spray head into the secondary drying chamber. The repeated contact of the partially dried material under partial vacuum with the heated oil causes further but less vigorous expansion, agitation and evolution of moisture. The maerial is progressed through the dryer in an average residence time of 10 minutes and after discharge is centrifuged to subject the material to 150 to 250 Us to remove excess fat. Again, the material maintains substantially the size, shape and appearance of the original material. It has a moisture content of about 4 percent and a very slight oily feed.

It will be understood that the oil cannot be recycled for reuse continuously without replenishment, filtration, clarification and the like. However, since such expedients are well known and recognized in the art, this application is not burdened with excessive disclosure of what is old, but is directed primarily to applicants contribution to the art. Likewise, temperature and pressure gauges, level indicators and like accessories whose use in the art is well known and understood are not shown.

It is apparent that many modifications and variations of this invention as hereinbefore set forth may be made without departing from the spirit and scope thereof. The specific embodiments described are given by way of example only and the invent-ion is limited only by the terms of the appended claims.

I claim:

1. A method of dehydrating moist particulate solid material continuously under partial vacuum which comprises (A) introducing a stream of hot oil into a confined blending zone,

(B) entraining the material to be dried in said stream of hot oil in said blending zone,

(C) passing said mixture of material to be dried entrained in hot oil from said blending zone into a larger directly communicating expansion zone maintained under partial vacuum,

(D) withdrawing vaporized moisture evolved fromsaid material in said expansion zone,

(E) collecting said resulting dehydrated material and oil in a collection zone at the bottom of said expansion zone,

(F) removing the dehydrated material and oil from said collection zone while maintaining the partial vacuum therein, and

(G) separating the excess oil from the dehydrated material.

2. A method according to claim 1 further characterized in that said mixture of particulate material to be dried entrained in said hot oil stream is introduced tangentially into the top of said expansion zone.

3. A method according to claim 1 further characterized in that said solid material and oil is held in said collection zone and subjected to further heating therein.

4. A method according to claim 1 further characterized in that said excess oil is separated from the dehydrated material by centrifugation.

5. A method according to claim 1 further characterized in that said dehydrated material after discharge from said expansion zone is subjected to further drying by repeatedly contacting said material with hot oil under partial vacuum.

6. A method according to claim 5 further characterized in that said oil is simultaneously drained from the dehydrated material.

7. A method according to claim 5 further characterized in that said oil is applied by spraying at a plurality of locations along the flow path of the solid material.

8. Apparatus for dehydrating moist particulate solid material continuously under partial vacuum which comprises (A) a confined blending chamber,

(B) oil feed means for introducing a stream of hot oil into said chamber,

(C) material feed means for introducing solid material to be dried into said chamber into entrainment in said oil stream,

(D) a large expansion chamber in direct communication with said blending chamber at the end thereof opposite from said oil feed means,

(E) means for maintaining said expansion chamber under partial vacuum and for withdrawing vapors therefrom,

(F) a collection zone in the bottom of said chamber,

and

(G) vacuum-tight seal and discharge means in the bottom of said collection zone.

9. Apparatus according to claim 8 further characterized in that said expansion chamber is a cyclone.

10. Apparatus according to claim 9 further characterized in that said blending chamber is a tangential inlet to said cyclone.

11. Apparatus according to claim 8 further characterized in that the collection zone of said expansion chamber is provided with auxiliary heating means.

12. Apparatus according to claim 8 further characterized in that means are provided for separation of excess oil from the dehydrated solid material after discharge from the collection zone of said expansion chamber.

13. Apparatus according to claim 8 further characterized by the provision of a secondary drying stage comprising (H) an elongated secondary drying vessel in direct communication at one end with the discharge means from said expansion chamber,

(1) means for maintaining said vessel under partial vacuum and withdrawing vapors therefrom,

(J) oil feed means for introducing hot oil to said vessel at a plurality of locations along the length of said vessel,

(K) means for advancing solid material through said vessel,

(L) drainage means along the bottom of said vessel for removal of excess oil therefrom, and

(M) vacuum-tight seal and material discharge means at the opposite end of said vessel.

References (Jited by the Examiner UNITED STATES PATENTS 703,393 7/1902 Edson 34-9 1,772,222 8/1930 Mueller 34- 8 3,194,670

7/1965 Dorsey 99 199 WILLIAM J. WYE, Primary Examiner. 

1. A METHOD OF DEHYDRATING MOIST PARTICULATE SOLID MATERIAL CONTINUOUSLY UNDER PARTIAL VACUUM WHICH COMPRISES (A) INTRODUCING A STREAM OF HOT OIL INTO A CONFINED BLENDING ZONE, (B) ENTRAINING THE MATERIAL TO BE DRIED IN SAID STREAM OF HOT OIL IN SAID BLENDING ZONE, (C) PASSING SAID MIXTURE OF MATERIAL TO BE DRIED ENTRAINED IN HOT OIL FROM SAID BLENDING ZONE INTO A LARGER DIRECTLY COMMUNICATING EXPANSION ZONE MAINTAINED UNDER PARTIAL VACUUM, (D) WITHDRAWING VAPORIZED MOISTURE EVOLVED FROM SAID MATERIAL IN SAID EXPANSION ZONE, (E) COLLECTING SAID RESULTING DEHYDRATED MATERIAL AND OIL IN A COLLECTION ZONE AT THE BOTTOM OF SAID EXPANSION ZONE, (F) REMOVING THE DEHYDRATED MATERIAL AND OIL FROM SAID COLLECTION ZONE WHILE MAINTAINING THE PARTIAL VACUUM THEREIN, AND (G) SEPARATING THE EXCESS OIL FROM THE DEHYDRATED MATERIAL. 